A document reading apparatus such as the scanner of a photocopier is generally equipped with a platen glass on which a document to be read is placed, and a document cover for bringing the mounted document in close contact with the platen glass.
In the field of document reading apparatuses, many proposals have been disclosed on the art of detecting an open/close operation of the document cover. They are disclosed, for example, in Japanese Unexamined Patent Application Publication No. H 06-309449, Japanese Unexamined Patent Application Publication No. 2004-357007, and Japanese Unexamined Patent Application Publication No. 2009-239929.
According to the technique described in Japanese Unexamined Patent Application Publication No. H 06-309449, the output value of a CCD sensor is monitored. The open/close operation of the document cover is detected by detecting the output of the CCD sensor to be increased by the light inside the room when the document cover is opened.
According to the technique disclosed in Japanese Unexamined Patent Application Publication No. 2004-357007, a control section inside the scanner determines, based on the detection signal value from the external light sensor, whether the intensity of the detected external light has been increased or not, and decreased or not, so that the open/close operation of document cover is detected.
Further, according to the technique introduced in Japanese Unexamined Patent Application Publication No. 2009-239929, a control section determines whether the document platen is being exposed to the external light or not, and the open/close operation of the document cover is thus detected.
However, with the method for detecting the open/close operation of the document cover disclosed in Japanese Unexamined Patent Application Publication No. H 06-309449, Japanese Unexamined Patent Application Publication No. 2004-357007, and Japanese Unexamined Patent Application Publication No. 2009-239929, the detection accuracy depends on the external environment, as exemplified by the case where detection accuracy deteriorates when the amount of external light is limited. Thus, the open/close operation of the document cover cannot be detected accurately.